It is known, e.g. as disclosed in EP 0225753A2 (University of California), to generate and sustain a low pressure discharge in a gas by using electromagnetic surface waves. Surface waves are created by an energizer (also known as a launcher) which is positioned around and external of, but not extending the whole length of, a discharge tube containing the gas. In such an arrangement, it is not necessary to provide electrodes inside the discharge tube. The power to generate the electromagnetic wave is provided by a radio frequency (r.f.) power generator.
It is proposed that such an arrangement be used as a visible light or a UV source. To provide a visible light source, the discharge tube could be a generic fluorescent lamp discharge tube containing a mix of inert gases and mercury vapour (e.g. argon gas and mercury vapour) and having on its inner surface a phosphor which converts 254 nm U.V. radiation to visible light. To provide a U.V. source, the discharge tube could be a generic germicidal or curing lamp discharge tube constructed of quartz glass and containing a mix of inert gases and mercury vapour, but with no phosphor.
Our copending British Patent Application (Agents Ref. PQ 50316) discloses such an arrangement in which the fill contains a metal halide. On excitation by a surface wave, a discharge is generated which produces visible light.